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Auto merge of #8981 - PrestonFrom:more_details_for_significant_drop_lint, r=flip1995

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Add details about how significant drop in match scrutinees can cause deadlocks

Adds more details about how a significant drop in a match scrutinee can cause a deadlock and include link to documentation.

changelog: Add more details to significant drop lint to explicitly show how temporaries in match scrutinees can cause deadlocks.
This commit is contained in:
bors 2022-06-29 13:23:21 +00:00
commit 90227c10f7
4 changed files with 390 additions and 100 deletions
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2
clippy_lints/src/matches/mod.rs
View file

@ -963,7 +963,7 @@ impl<'tcx> LateLintPass<'tcx> for Matches {
return;
}
if matches!(source, MatchSource::Normal | MatchSource::ForLoopDesugar) {
significant_drop_in_scrutinee::check(cx, expr, ex, source);
significant_drop_in_scrutinee::check(cx, expr, ex, arms, source);
}
collapsible_match::check_match(cx, arms);

162
clippy_lints/src/matches/significant_drop_in_scrutinee.rs
View file

@ -1,10 +1,10 @@
use crate::FxHashSet;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::get_attr;
use clippy_utils::source::{indent_of, snippet};
use clippy_utils::{get_attr, is_lint_allowed};
use rustc_errors::{Applicability, Diagnostic};
use rustc_hir::intravisit::{walk_expr, Visitor};
use rustc_hir::{Expr, ExprKind, MatchSource};
use rustc_hir::{Arm, Expr, ExprKind, MatchSource};
use rustc_lint::{LateContext, LintContext};
use rustc_middle::ty::subst::GenericArgKind;
use rustc_middle::ty::{Ty, TypeAndMut};
@ -16,12 +16,23 @@ pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'tcx>,
scrutinee: &'tcx Expr<'_>,
arms: &'tcx [Arm<'_>],
source: MatchSource,
) {
if is_lint_allowed(cx, SIGNIFICANT_DROP_IN_SCRUTINEE, expr.hir_id) {
return;
}
if let Some((suggestions, message)) = has_significant_drop_in_scrutinee(cx, scrutinee, source) {
for found in suggestions {
span_lint_and_then(cx, SIGNIFICANT_DROP_IN_SCRUTINEE, found.found_span, message, |diag| {
set_diagnostic(diag, cx, expr, found);
let s = Span::new(expr.span.hi(), expr.span.hi(), expr.span.ctxt(), None);
diag.span_label(s, "temporary lives until here");
for span in has_significant_drop_in_arms(cx, arms) {
diag.span_label(span, "another value with significant `Drop` created here");
}
diag.note("this might lead to deadlocks or other unexpected behavior");
});
}
}
@ -80,22 +91,77 @@ fn has_significant_drop_in_scrutinee<'tcx, 'a>(
let mut helper = SigDropHelper::new(cx);
helper.find_sig_drop(scrutinee).map(|drops| {
let message = if source == MatchSource::Normal {
"temporary with significant drop in match scrutinee"
"temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression"
} else {
"temporary with significant drop in for loop"
"temporary with significant `Drop` in `for` loop condition will live until the end of the `for` expression"
};
(drops, message)
})
}
struct SigDropChecker<'a, 'tcx> {
seen_types: FxHashSet<Ty<'tcx>>,
cx: &'a LateContext<'tcx>,
}
impl<'a, 'tcx> SigDropChecker<'a, 'tcx> {
fn new(cx: &'a LateContext<'tcx>) -> SigDropChecker<'a, 'tcx> {
SigDropChecker {
seen_types: FxHashSet::default(),
cx,
}
}
fn get_type(&self, ex: &'tcx Expr<'_>) -> Ty<'tcx> {
self.cx.typeck_results().expr_ty(ex)
}
fn has_seen_type(&mut self, ty: Ty<'tcx>) -> bool {
!self.seen_types.insert(ty)
}
fn has_sig_drop_attr(&mut self, cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
if let Some(adt) = ty.ty_adt_def() {
if get_attr(cx.sess(), cx.tcx.get_attrs_unchecked(adt.did()), "has_significant_drop").count() > 0 {
return true;
}
}
match ty.kind() {
rustc_middle::ty::Adt(a, b) => {
for f in a.all_fields() {
let ty = f.ty(cx.tcx, b);
if !self.has_seen_type(ty) && self.has_sig_drop_attr(cx, ty) {
return true;
}
}
for generic_arg in b.iter() {
if let GenericArgKind::Type(ty) = generic_arg.unpack() {
if self.has_sig_drop_attr(cx, ty) {
return true;
}
}
}
false
},
rustc_middle::ty::Array(ty, _)
| rustc_middle::ty::RawPtr(TypeAndMut { ty, .. })
| rustc_middle::ty::Ref(_, ty, _)
| rustc_middle::ty::Slice(ty) => self.has_sig_drop_attr(cx, *ty),
_ => false,
}
}
}
struct SigDropHelper<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
is_chain_end: bool,
seen_types: FxHashSet<Ty<'tcx>>,
has_significant_drop: bool,
current_sig_drop: Option<FoundSigDrop>,
sig_drop_spans: Option<Vec<FoundSigDrop>>,
special_handling_for_binary_op: bool,
sig_drop_checker: SigDropChecker<'a, 'tcx>,
}
#[expect(clippy::enum_variant_names)]
@ -118,11 +184,11 @@ impl<'a, 'tcx> SigDropHelper<'a, 'tcx> {
SigDropHelper {
cx,
is_chain_end: true,
seen_types: FxHashSet::default(),
has_significant_drop: false,
current_sig_drop: None,
sig_drop_spans: None,
special_handling_for_binary_op: false,
sig_drop_checker: SigDropChecker::new(cx),
}
}
@ -163,7 +229,7 @@ impl<'a, 'tcx> SigDropHelper<'a, 'tcx> {
if self.current_sig_drop.is_some() {
return;
}
let ty = self.get_type(expr);
let ty = self.sig_drop_checker.get_type(expr);
if ty.is_ref() {
// We checked that the type was ref, so builtin_deref will return Some TypeAndMut,
// but let's avoid any chance of an ICE
@ -187,14 +253,6 @@ impl<'a, 'tcx> SigDropHelper<'a, 'tcx> {
}
}
fn get_type(&self, ex: &'tcx Expr<'_>) -> Ty<'tcx> {
self.cx.typeck_results().expr_ty(ex)
}
fn has_seen_type(&mut self, ty: Ty<'tcx>) -> bool {
!self.seen_types.insert(ty)
}
fn visit_exprs_for_binary_ops(
&mut self,
left: &'tcx Expr<'_>,
@ -214,44 +272,15 @@ impl<'a, 'tcx> SigDropHelper<'a, 'tcx> {
self.special_handling_for_binary_op = false;
}
fn has_sig_drop_attr(&mut self, cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
if let Some(adt) = ty.ty_adt_def() {
if get_attr(cx.sess(), cx.tcx.get_attrs_unchecked(adt.did()), "has_significant_drop").count() > 0 {
return true;
}
}
match ty.kind() {
rustc_middle::ty::Adt(a, b) => {
for f in a.all_fields() {
let ty = f.ty(cx.tcx, b);
if !self.has_seen_type(ty) && self.has_sig_drop_attr(cx, ty) {
return true;
}
}
for generic_arg in b.iter() {
if let GenericArgKind::Type(ty) = generic_arg.unpack() {
if self.has_sig_drop_attr(cx, ty) {
return true;
}
}
}
false
},
rustc_middle::ty::Array(ty, _)
| rustc_middle::ty::RawPtr(TypeAndMut { ty, .. })
| rustc_middle::ty::Ref(_, ty, _)
| rustc_middle::ty::Slice(ty) => self.has_sig_drop_attr(cx, *ty),
_ => false,
}
}
}
impl<'a, 'tcx> Visitor<'tcx> for SigDropHelper<'a, 'tcx> {
fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
if !self.is_chain_end && self.has_sig_drop_attr(self.cx, self.get_type(ex)) {
if !self.is_chain_end
&& self
.sig_drop_checker
.has_sig_drop_attr(self.cx, self.sig_drop_checker.get_type(ex))
{
self.has_significant_drop = true;
return;
}
@ -330,3 +359,38 @@ impl<'a, 'tcx> Visitor<'tcx> for SigDropHelper<'a, 'tcx> {
}
}
}
struct ArmSigDropHelper<'a, 'tcx> {
sig_drop_checker: SigDropChecker<'a, 'tcx>,
found_sig_drop_spans: FxHashSet<Span>,
}
impl<'a, 'tcx> ArmSigDropHelper<'a, 'tcx> {
fn new(cx: &'a LateContext<'tcx>) -> ArmSigDropHelper<'a, 'tcx> {
ArmSigDropHelper {
sig_drop_checker: SigDropChecker::new(cx),
found_sig_drop_spans: FxHashSet::<Span>::default(),
}
}
}
fn has_significant_drop_in_arms<'tcx, 'a>(cx: &'a LateContext<'tcx>, arms: &'tcx [Arm<'_>]) -> FxHashSet<Span> {
let mut helper = ArmSigDropHelper::new(cx);
for arm in arms {
helper.visit_expr(arm.body);
}
helper.found_sig_drop_spans
}
impl<'a, 'tcx> Visitor<'tcx> for ArmSigDropHelper<'a, 'tcx> {
fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
if self
.sig_drop_checker
.has_sig_drop_attr(self.sig_drop_checker.cx, self.sig_drop_checker.get_type(ex))
{
self.found_sig_drop_spans.insert(ex.span);
return;
}
walk_expr(self, ex);
}
}